Inferred water analysis in polyphenylene sulfide production

ABSTRACT

A method for producing polyphenylene sulfide (PPS) polymer, including polymerizing reactants in a reaction mixture in a vessel to form PPS polymer in the vessel, measuring values of operating variables of the vessel and/or PPS process, and determining the amount of quench fluid to add to the vessel based on the values of the operating variables. The technique may rely on the vapor liquid equilibrium (VLE) of the mixture to calculate the concentration of water existing in the reactor prior to quench, and accounts for the effectiveness of the upstream dehydration process and in the amount of water produced during the polymerization. The technique is a striking improvement over the trial-and-error estimation of the amount of quench water based on human operating experience, and avoids direct measurements of the existing water concentration in the reactor. The result is improved control of PPS particle size and other properties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present technique relates generally to production of polyphenylenesulfide (PPS). In particular, the present technique relates todetermining water content in a PPS reactor based on reactor variables.

2. Description of the Related Art

This section is intended to introduce the reader to various aspects ofart which may be related to various aspects of the present inventionthat are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentinvention. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

Polyphenylene sulfide (PPS), also known as poly(arylene) sulfide, is ahigh-performance engineering thermoplastic that may be heated and moldedinto desired shapes in a variety of manufacturing, commercial, andconsumer applications. PPS may be used in the preparation of fibers,films, coatings, injection molding compounds, and fiber-reinforcedcomposites, and is well-suited for demanding applications in appliance,automotive, and electrical/electronic industries. PPS may beincorporated as a manufacturing component either alone or in a blendwith other materials, such as elastomeric materials, copolymers, resins,reinforcing agents, additives, other thermoplastics, and the like.Initially, PPS was promoted as a replacement for thermosettingmaterials, but has become a very suitable molding material, especiallywith the addition of glass and carbon fibers, minerals, fillers, and soforth. In fact, PPS is one of the oldest high-performanceinjection-molding plastics in the polymer industry, with non-filledgrades commonly extruded as coatings.

PPS polymer, including semi-crystalline PPS, is an attractiveengineering plastic because, in part, it provides an excellentcombination of properties. For example, PPS provides for resistance toaggressive chemical environments while also providing for precisionmolding to tight tolerances. Further, PPS is thermally stable,inherently non-flammable without flame retardant additives, andpossesses excellent dielectric/insulating properties. Other propertiesinclude dimensional stability, high modulus, and creep resistance. Thebeneficial properties of PPS are due, in part, to the stable chemicalbonds of its molecular structure, which impart a relatively high degreeof molecular stability, for example, toward both thermal degradation andchemical reactivity.

The general molecular structure of PPS is a polymer composed ofalternating aromatic (phenylene) rings and sulfur atoms (in a parasubstitution pattern), as shown below.

The molecular structure may readily pack into a thermally stablecrystalline lattice, giving PPS that is a semi-crystalline polymer witha high crystalline melting point of up to about 285° C. and higher.Because of its molecular structure, PPS also tends to char duringcombustion, making the material inherently flame retardant, asmentioned. Further, the material will typically not dissolve in solventsat temperatures below about 200° C.

Though PPS was first discovered in the late 19th century, many engineersfailed in their attempts over the years to produce PPS for industrialuse, and thus the history of PPS as an industrial material is relativelyshort. In 1967, however, Phillips Petroleum Company of Bartlesville,Okla. devised a method for producing PPS through the synthesis ofpara-dichlorobenzene and sodium sulfide, as described below.

This condensation polymerization (or step polymerization) marked thebeginning of industrial-scale commercialization of PPS. In 1972,Phillips Petroleum Company began commercial-scale production of PPS, andthis PPS was soon noted for having an effective balance of thermal andchemical resistances, nonflammability, and electrical properties. Today,PPS is manufactured and sold under the trade name Ryton® by ChevronPhillips Chemical Company LP of The Woodlands, Tex.

In general, PPS may be prepared by reacting a dihalogenated aromaticcompound with a sulfur source under polymerization conditions in thepresence of a polar organic compound. The polar organic compound, suchas N-methyl pyrrolidone (NMP), is generally an organic solvent thatmaintains the reactants and PPS polymer in solution during thepolymerization. A molecular weight modifying agent, such as an alkalimetal salt, may be optionally added to the polymerization mixture.Typically, the polymerization reaction mixture comprises aqueous andorganic phases, with the PPS polymer dissolved primarily in the organicphase. Generally, after the majority of reactants have polymerized, thereaction mixture may be cooled to terminate the polymerization and todrop the PPS polymer solid from solution. Such cooling of thepolymerization may be accomplished, for example, by reducing thepressure of the reaction mixture to flash the polar organic compound(e.g., NMP), or by adding more NMP to the mixture to cool (quench) themixture. The choice of flashing the existing NMP or quenching with moreNMP may depend upon the design of the particular manufacturing plant, aswell as the particular grade of PPS. Moreover, the choice may affect theprocess economics, as well as the polymer bulk properties, morphology,particle size, and the like.

Another process alternative in the termination step is to cool (orquench) the polymerization by adding water to the reaction mixture. Awater quench, relative to an NMP quench, typically results in a largerparticle size of the PPS, which may facilitate separation of the PPSproduct from undesirable solid components formed in the polymerizationsince the undesirable components, e.g., residual salt and slime,typically have a relatively small particle size. A problem with waterquench, however, is that if too much water is added, the PPS particlesize (average diameter) may become too large for downstreamseparation/handling equipment, resulting in damage or shutdown of theequipment, off-spec production of PPS, contamination of the PPS, and soforth. Conversely, if too little water is added, the PPS particle sizemay be too small, resulting in losses of PPS escaping with the separatedstream of undesirable components.

To complicate matters, the amount of water existing in the reactorimmediately prior to quench varies and is typically unknown.Furthermore, it is the total amount of water in the reactor, and notjust the amount of quench water added, that affects the PPS properties.Water may exist in the reactor prior to quench because of inefficienciesin the upstream dehydration of the feedstock entering the reactor andbecause water may be a product of the PPS (condensation) polymerizationin the reactor.

General correlations are known between the total amount water in thereactor during quench versus the generated PPS particle size, but again,the determination of how much quench water to add is problematic becausethe amount (and concentration) of existing water is typically unknown.In the PPS manufacturing process, the human operator typically guesses,based on experience, trial-and-error, “feel” of the operatingconditions, and so forth, as to how much water exists in the reactor andas to how much quench water to add.

It should be noted that laboratory or on-line sampling of the reactormixture to test for the water content may be problematic due to theharsh reactor conditions. Further, it may be difficult to obtain arepresentative sample of the reaction mixture which may comprisepartially-dispersed aqueous and organic phases. Also, testing may beexpensive and time-consuming. Moreover, during sampling and analysis,the polymerization may proceed and conditions may change, sometimesundesirably.

Lastly, it should be explained that the PPS polymer may remainsubstantially dissolved in the reactor solution even after the quenchliquid is added. In this case, after the quench liquid is added, thereactor contents may be cooled with a reactor coolant system toprecipitate the PPS. If the right amount or type of quench liquid is notadded initially, the PPS particles that drop from solution during thecontrolled cooling may not be the desired size. Generally, there is nota second chance to adjust the amount of quench water or the particlesize of the PPS polymer.

In conclusion, the determination of the amount of water existing in thereactor prior to quench is problematic because, in part, other liquidcomponents, such as NMP, are present. Thus, a conventional volumetricmeasurement, for example, such as through the use of reactor levelindication, gives the volume of the mixture and not just the volume ofthe water. There is a need, therefore, for a technique to determine theamount of water existing in the reactor prior to quench (or cool down)of the reaction. The technique should further determine how much quenchwater to add to the reaction mixture to control the total amount ofwater in the reactor during quench to give the desired particle size andother properties of the PPS.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the invention may become apparent upon reading thefollowing detailed description and upon reference to the drawings inwhich:

FIG. 1 is a block flow diagram depicting an exemplary system forproducing polyphenylene sulfide (PPS) in accordance with one embodimentof the present techniques;

FIG. 2 is a diagrammatical representation of the polymerization reactordepicted in FIG. 1 in accordance with one embodiment of the presenttechniques;

FIG. 3 is a block diagram of an exemplary method for PPS polymerizationand subsequent quenching in accordance with one embodiment of thepresent techniques;

FIG. 4 is a block diagram of an exemplary method for determining theamount of quench water to add at the conclusion of a PPS polymerizationin accordance with one embodiment of the present techniques;

FIG. 5 is a plot of the calculated value for the mole fraction increaseof water in the reactor versus the amount of quench water added, inaccordance with one embodiment of the present techniques; and

FIG. 6 is a plot of the average diameter of the PPS particle size inmicrons as a function of reactor agitation speed in revolutions perminute (RPM) and a function of the mole fraction of water in the reactorduring quench, in accordance with one embodiment of the presenttechniques.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

In order to facilitate presentation of the present technique, thedisclosure is broken into a number of sections. Section I introduces thePPS process and techniques for determining the amount of quench water.Section II discusses components and conditions of exemplary PPSpolymerization mixtures. Section III discusses equipment and methodsemployed in the exemplary production of PPS, as well as, applicationsand end-uses of the PPS polymer. Finally, Section IV discussestechniques for the determination of the amount of quench water to add tothe PPS polymerization reactor to give the desired PPS particle size.

I. Introduction

It was established early in the development of the PPS water quenchprocess that the total amount of water in the PPS polymerization reactorduring the water quench is important to the control of the polymerparticle size, bulk density, and fines generation, and other propertiesof the PPS polymer. It is generally known for the various grades andtypes of PPS, the relationship between the amount (i.e., pounds,gallons, or concentration) of total water in the reactor during quenchversus the PPS particle size (i.e., average diameter in microns). Aproblem is that the amount of water (and concentration of water) in thepolymerization reactor immediately prior to quench is typically unknownto the operator. In response, the present technique can calculate theapproximate water content in the polymerization reactor prior to quench,and can provide the correct amount of quench water to add to the reactorto yield the desired PPS particle size (expressed as an average ormedian particle size, a particles size distribution, and so on). Asdiscussed below, the technique utilizes information about the vaporliquid equilibrium (VLE) of the polymerization mixture to calculate theconcentration of water existing in the reactor prior to quench. Thecalculation may be based on reactor system variables, e.g., reactortemperature and pressure, and accounts for variations, for example, inthe effectiveness of the upstream dehydration process and in the amountof water produced during the polymerization.

In one embodiment, the liquid mixture in the reactor 14 is assumed to bean ideal binary mixture of water and NMP, and the vapor phase is assumedsaturated, i.e., the liquid and vapor phases are assumed to be inequilibrium. With these assumptions, and with reactor pressure andreactor temperature as inputs, Raoult's Law may be used to calculate theconcentration of water (x_(A)) in the reactor mixture:

Raoult's Law

P=P° _(A)×_(A) +P° _(B)×_(B)where P is the total pressure in the reactor (a measured value), P°_(A)and P°_(B) are the pure-component vapor pressures of water and NMP,respectively, and x_(A) and x_(B) are the liquid mole fractions of waterand NMP, respectively. As discussed below, the pure-component vaporpressures may be calculated using a suitable vapor pressure equation,such as Antoine's equation, with reactor temperature as an input.Finally, because the mixture is assumed binary, the expression (1−x_(A))may be substituted for x_(B), and thus x_(A), the mole fraction ofwater, may be solved. With the mole fraction of water determined, theamount of water existing in the reactor may then be calculated based onthe liquid volume in the reactor. The amount of quench water may then bedetermined based on the desired total amount of water that gives thedesire PPS particle size.

The technique is a striking improvement over the trial-and-errorestimation of the amount of quench water based on human operatingexperience, and avoids the drawbacks associated with direct measurementof the existing water concentration in the reactor. The result isimproved and more effective control of the average diameter or particlesize (or particle size distribution) of PPS in the polymerizationreactor. The technique generally avoids the generation of undesirablysmall particles of PPS and thus facilitates separation of the prime PPSproduct from the reject material, such as salt and slime, which tend tohave a smaller particle size. Further, the improved control of particlesize lowers the generation of undesirably large particles that maydamage downstream separation equipment and that may result in increaseddowntime and increased maintenance costs. In sum, the technique providesfor improved PPS product quality, reduced PPS losses, reduced downtime,reduced operating and maintenance costs, and so forth.

II. Polymerization of Polyphenylene Sulfide (PPS)

A. Components of the PPS Polymerization Reaction Mixture

PPS polymers may be produced generally by contacting underpolymerization conditions at least one dihaloaromatic compound, a sulfursource, and a polar organic compound.

1. PPS Polymerization Reactants

Two primary reactants are the dihaloaromatic compound and the sulfursource.

a. Dihaloaromatic Compound as a PPS Reactant

Some of the dihaloaromatic compounds which may be employed may berepresented by the formula:

where each X may be selected from chlorine, bromine, and iodine, andeach R may be selected from hydrogen and hydrocarbyl in which thehydrocarbyl can be an alkyl, cycloalkyl, or aryl radical or combinationthereof such as alkaryl, aralkyl, or the like, the total number ofcarbon atoms in each molecule being within the range of 6 to about 24.While the halogen atoms can be in any position in the dihaloaromaticcompound, it is common in the art to employ p-dihalobenzenes as thedihaloaromatic compound. Examples of p-dihalobenzenes that may be usedinclude p-dichlorobenzene (DCB), p-dibromobenzene, p-diiodobenzene,1-chloro-4-bromobenzene, 1-chloro-4-iodobenzene, 1-bromo-4-iodobenzene,2,5-dichlorotoluene. 2,5-dichloro-p-xylene,1-ethyl-4-isopropyl-2,5-dibromobenzene,1,2,4,5-tetramethyl-3,6-dichlorobenzene,1-butyl-4-cyclohexyl-2,5-dibromo-benzene,1-hexyl-3-dodecyl-2,5-dichlorobenzene, 1-octadecyl-2,5-diidobenzene,1-phenyl-2-chloro-5-bromobenzene, 1-(p-tolyl)-2,5-dibromobenzene,1-benzyl-2,5-dichlorobenzene,1-octyl-4-(3-methylcyclopentyl)-2,5-dichloro-benzene, and the like, andmixtures of any two or more thereof. A typical dihaloaromatic compoundemployed in the polymerization of PPS is p-dichlorobenzene (DCB) due toits availability and effectiveness.b. A Sulfur Source as a PPS Reactant

Sulfur sources which may be employed in the PPS polymerization processinclude, for example, thiosulfates, thioureas, thioamides, elementalsulfur, thiocarbamates, metal disulfides and oxysulfides,thiocarbonates, organic mercaptans, organic mercaptides, organicsulfides, alkali metal sulfides and bisulfides, hydrogen sulfide, andthe like. It is common in the art to use an alkali metal sulfide as thesulfur source, which may include lithium sulfide, sodium sulfide,potassium sulfide, rubidium sulfide, cesium sulfide, and mixturesthereof. Generally, the alkali metal sulfide may be used as a hydrate oras an aqueous mixture. For an aqueous mixture, as discussed below, thealkali metal sulfide can be prepared by the reaction of an alkali metalhydroxide with an alkali metal bisulfide in aqueous solution. A commonalkali metal sulfide used as the sulfur source in PPS polymerization issodium sulfide (Na2S), which may be prepared by combining sodiumhydrosulfide (NaSH) and sodium hydroxide (NaOH) in an aqueous solutionfollowed by dehydration.

2. Polar Organic Compounds (Including Organic Solvents)

Useful polar organic compounds in the production of the PPS polymers aretypically those that are solvents for the dihaloaromatic compounds andthe sulfur source, and thus those that keep the dihaloaromatic compoundsand sulfur source in solution during the polymerization. In general,examples of such polar organic compounds include amides, includinglactams, and sulfones. In particular, the polar organic compounds mayinclude hexamethylphosphoramide, tetramethylurea,N,N′-ethylenedipyrrolidone, N-methyl-2-pyrrolidone, pyrrolidone,caprolactam, N-ethylcaprolactam, sulfolane, N,N′-dimethylacetamide,1,3-dimethyl-2-imidazolidinone, low molecular weight polyamides, and thelike. The polar organic compound typically used isN-methyl-2-pyrrolidone (NMP).

3. Other Components (Including Additional Reactants)

Other components may be employed in the polymerization reaction mixtureand/or during the polymerization. For example, molecular weightmodifying or enhancing agents such as alkali metal carboxylates, lithiumhalides, or water can be added or produced during polymerization. Alkalimetal carboxylates which may be employed include those having theformula R′CO2M where R′ is a hydrocarbyl radical selected from alkyl,cycloalkyl, aryl, alkylaryl, arylalkyl, and the number of carbon atomsin R′ is in the range of 1 to about 20, and M is an alkali metalselected from lithium, sodium, potassium, rubidium and cesium. Thealkali metal carboxylate may be employed as a hydrate or as a solutionor dispersion in water. A commonly-used alkali metal carboxylate in thePPS process is sodium acetate (NaOAC) due to its availability andeffectiveness.

Additionally, reactants, such as comonomers, may be included as well.Such comonomers typically include polyhaloaromatic compounds having morethan two halogen atoms, such as trichlorobenzene. For example,polyhalo-substituted aromatic compounds having more than two halogensubstitutions may be employed as reactants in order to prepare branched,relatively high molecular weight poly(arylene sulfide) polymers. It iscommon in the art to use 1,2,4-trichlorobenzene (TCB) as thepolyhalo-substituted compound when employed.

Further, a base may be employed as a reactant, for example, where thesulfur source employed is an alkali metal bisulfide. If a base is used,alkali metal hydroxides, such as sodium hydroxide (NaOH), may typicallybe utilized. Additionally, an acidic solution may be added to thereaction mixture prior to termination of the polymerization to reducethe basicity of the reaction mixture. Such a reduction in basicity maylower the amount of ash-causing polymer impurities in the PPS polymer.

B. Conditions of the PPS Polymerization Reaction Mixture

1. Ratio of Reactants

Generally, the ratio of reactants employed in the polymerization processmay vary widely. However, the typical molar ratio of dihaloaromaticcompound to sulfur source is generally in the range of about 0.8 toabout 2, and more commonly from 0.95 to 1.3. The amount ofpolyhalo-substituted aromatic compound optionally employed as a reactantmay be that amount to achieve the desired degree of branching to givethe desired polymer melt flow. Generally, about 0.0004 to 0.02 moles ofpolyhalo-substituted aromatic compound per mole of dihaloaromaticcompound may be employed. If an alkali metal carboxylate is employed asa molecular weight modifying agent, the mole ratio of alkali metalcarboxylate to dihaloaromatic compounds may be generally within therange of about 0.02 to about 4, more commonly from about 0.1 to 2.

2. Ratio of Solvent and Base to the Sulfur Source

The amount of polar organic compound employed may also vary during thepolymerization over a wide range. However, the molar ratio of polarorganic compound to the sulfur source is typically within the range ofabout 1 to 10. If a base, such as sodium hydroxide, is contacted withthe polymerization reaction mixture, the molar ratio is generally in therange of about 0.5 to about 4 moles per mole of sulfur source.

3. Reaction Conditions

The components of the reaction mixture can be contacted with each otherin any order. Some of the water, which may be introduced with thereactants, may be removed prior to polymerization, such as in adehydration process, especially if a significant amount of water (e.g.,more than 0.3 moles per mole of sulfur source) is present. Moreover, thetemperature at which the polymerization is conducted is generally withinthe range of about 170° C. (347° F.) to about 450° C. (617° F.), morecommonly from about 235° C. to about 350° C. Further, the reaction timemay vary widely, depending, in part, on the reaction temperature, but isgenerally within the range of about 10 minutes to 3 days, more commonlyfrom about 1 hour to about 8 hours. Typically, the reactor pressure needbe only sufficient to maintain the polymerization reaction mixturesubstantially in the liquid phase. Such pressure will generally be inthe range of about 0 pounds per square inch gauge (psig) to about 400psig, more commonly about 150 psig to about 250 psig.

C. Termination of the Polymerization Reaction and Recovery of them PPS

The polymerization may be terminated to begin recovery of the PPS fromthe reaction mixture by cooling the reaction mixture (removing heat) toa temperature below that at which substantial polymerization takes place(about 235° C.). The polymerization reaction mixture may be cooled, forexample, by flashing the polar organic compound (e.g., NMP).Alternatively, the reaction mixture may be cooled by quenching, such asby adding more polar organic compound or by adding water to the reactionmixture. The reaction may also be terminated in a variety of other ways,such as by contacting the reaction mixture with a polymerizationinhibiting compound. It should be clarified that termination of thepolymerization does not imply that complete reaction of thepolymerization components has occurred. Moreover, termination of thepolymerization is not meant to imply that no further polymerization ofthe reactants can take place. Generally, for economic reasons,termination (and PPS polymer recovery) may be initiated at a time whenpolymerization is substantially completed, that is, when the increase inpolymer molecular weight which would result from further polymerizationis not significant.

For recovery of the polymer, the cooling and termination of the reactionbrings the PPS polymer solids out of solution, which may then beseparated from the reaction mixture by conventional procedures. Suchprocedures include, for example, filtration of the polymer followed bywashing with water, or dilution of the reaction mixture with waterfollowed by filtration and water washing of the polymer. In general, thepolymers may be recovered by the “flash” process, by employing aseparation agent, by mechanical separation, and so forth.

The recovered PPS polymer may be further processed. For example, the PPSmay be cured through cross linking and/or chain extension by heating attemperatures above about 480° C. in the presence of freeoxygen-containing gas. Agents that affect crosslinking, such asperoxides, crosslinking accelerants, and/or crosslinking inhibitors, maybe incorporated into the PPS. Such cured PPS polymer generally has highthermal stability and good chemical resistance, and are useful, forexample, in the production of coatings, films, molded objects andfibers. Additionally, the PPS polymer may ultimately be blended withvarious additives, such as polymers, fiber reinforcements, fillers,pigments, nucleating agents, antioxidants, UV stabilizers, heatstabilizers, carbon black, metal deactivators, lubricants, plasticizers,corrosion inhibitors, mold release agents, pigments, titanium dioxide,clay, mica, processing aids, adhesives, tackifiers, and the like.Ultimately, the PPS polymer may be formed or molded into a variety ofcomponents or products for a diverse range of applications andindustries. Such components and products may be further processed,assembled, shipped, etc. prior to receipt by an end-user.

It should be clarified that the PPS polymer, in both flash and quenchprocesses, is generally in solution prior to termination of thepolymerization in the reactor. In the flash process, the reactorsolution may be charged to a flash vessel where the NMP is flashed off,leaving the PPS polymer, as well as salt and other undesirablecomponents. Thus, it is the flash process that facilitates precipitationof the PPS. In the quench process, however, the PPS polymer may remainin solution even after quench NMP or quench water is added to thereactor. Therefore, the reactor solution may be further cooled at acontrolled rate via a coolant system, for example, to cause the PPS tocome out of solution. However, it is the amount of quench water addedthat effects the particle size distribution of the PPS. In general,higher water content in the reaction mixture results in larger PPSparticles precipitating from the reaction mixture during the controlledcooling.

D. Examples of the PPS Polymerization

1. First Example of PPS Polymerization

A PPS polymer may be prepared by mixing 32.40 kg (71.42 lbs) of a 50% byweight sodium hydroxide (NaOH) aqueous solution with 39.34 kg (86.74lbs) of a solution containing 60% by weight sodium hydrosulfide (NaSH)and 0.4% by weight sodium sulfide (Na₂S). This solution, 11.34 kg (25lbs) of sodium acetate (NaOAc) powder, and 104.1 L (27.5 gal) ofN-methyl-2-pyrrolidone (NMP) may be added to a stirred (400 rpm)reactor, which may then be purged with nitrogen. This mixture may thenbe heated to about 172° C. (342° F.) and dehydrated to remove waterwhile the temperature is increased to about 211° C. (411° F.). Then,63.27 kg (139.49 lbs.) of p-dichlorobenzene (DCB) in 22.7 L (6 gals.) ofNMP may be charged to the reactor. The mixture may be heated to about282° C. (540° F.) and held at temperature for about 1.5 hours. Thereaction mixture may then be flashed at about 282° C. (540° F.) toremove the NMP and solidify the PPS polymer. The dry, salt-filledpolymer may be twice washed with 454.25 L (120 gal) of deionized waterat ambient temperature, then filtered, then washed with 302.83 L (80gal) of deionized water at 177° C. (350° F.) for 30 minutes. Thesolution may be filtered to recover approximately 26.76 kg (59 lbs) ofPPS.

2. Second Example of PPS Polymerization

This example also illustrates the general preparation of a PPS polymer.A mixture of 72.6 lbs of a 50 weight percent sodium hydroxide (NaOH)aqueous solution with 86.8 lbs of a 60 weight percent sodiumhydrosulfide (NaSH) aqueous solution may be prepared, and then addedwith 25 lbs of sodium acetate (NaOAc) powder, and 27.5 gal ofN-methyl-2-pyrrolidone (NMP) to a stirred (400 rpm) reactor. The reactormay be then purged with nitrogen, and the reaction mixture heated toremove water while the temperature increases to about 410° F. Then 135.9lbs of p-dichlorobenzene (DCB) and 6 gals of NMP may be charged to thereactor. The mixture may then be heated to about 460° F. and held attemperature for about 35 minutes, then was heated to 510° F. and heldfor 90 minutes, and then finally heated to 540° F.

The reaction mixture may then be removed from the reactor through acontrol valve into a vessel maintained at a pressure about 1 pounds persquare inch (psi) above atmospheric pressure, thereby resulting in thevaporization of most of the NMP and solidification of the PPS polymer.The dry, salt-filled polymer may then be twice washed with 120 gal ofdeionized water at ambient temperature, then filtered, then washed withabout 80 gal of deionized water containing 75 g calcium hydroxide at350° F. for 30 minutes. The solution may then be filtered to recover thePPS.

3. Third Example of PPS Polymerization

This example also describes the general preparation of a PPS polymer,according to known methods. In this typical PPS preparation, thefollowing may be added to a one-liter stirred stainless steel reactor:40.97 grams sodium hydroxide (NaOH) pellets of 98.6% purity (1.01 g-molNaOH) and 40.0 g double distilled water (2.22 g-mol), 95.49 g aqueoussodium bisulfide (NaSH) (58.707% NaSH by weight) (1.00 g-mol), and198.26 g of n-methyl-2-pyrrolidone (NMP) (2.00 g-mol). The reactor maybe degassed with 5 pressure release cycles of 50 psig nitrogen and 5cycles of 200 psig nitrogen. The reactor and contents may then be heatedslowly to 100° C., whereupon the dehydration outlet may be opened andnitrogen flow at the rate of 32 mL/min. initiated. The dehydration maycontinue while heating to a final temperature of about 204° C. Then thedehydration outlet may be closed and 148.49 g p-dichlorobenzene (DCB)(1.0 g-mol) dissolved in 1.00 g-mol NMP charged to the reactor using acharge cylinder. The charge cylinder was rinsed may be an additional 1g-mol of NMP which may also be added to the reactor. (The reactor maythen be degassed again in the same manner as described above). Further,the reactor may then be heated to polymerization conditions (235° C.)for 2 hours, then the temperature increased to 260° C. for 2 hours toproduce PPS.

At the conclusion of the polymerization, the reactor may be cooled toroom temperature and the mixture of PPS polymer and NMP may be extractedusing isopropanol. The reactor product may be washed with water sixtimes at 90° C. and filtered on a coarse filter paper to recover the PPSproduct which may be left to dry under a hood for 8-10 hours. The PPSproduct may then be placed in a vacuum oven and dried at 100° C. for 24hours to yield 101.23 g of dried PPS polymer product. The expectedextrusion rate of this PPS product is 72.71 g/10 min.

III. Production of Polyphenylene Sulfide (PPS)

Turning now to the drawings, and referring initially to FIG. 1, a blockflow diagram of an exemplary polyphenylene sulfide (PPS) manufacturingsystem generally designated by reference numeral 10 is depicted.

A. The Use of Water and NMP

In certain applications, such as in laboratory and pilot scalefacilities, the PPS manufacturing system 10 may be configured toaccommodate both flash termination (e.g., flash NMP) and quenchtermination (e.g., NMP or water). However, in general, commercial-scalePPS production facilities are typically designed toward one of flashtermination or quench termination. A flash termination design mayprovide for lower equipment and capital costs, as well as for morestraightforward operation. In contrast, quench plants may require moreequipment, but may give more versatility in operation and in theproduction of more diverse properties of the PPS polymer.

For a quench operation, the present techniques determine the amount ofwater 12 for quenching the reaction in the polymerization reactor 14 togive the desired average particle size and other properties of thepolymerized PPS. The water-quench cools the reaction and thus terminatesthe polymerization, and generally causes the PPS polymer which istypically dissolved in the organic phase to desirably precipitate andfall out of solution. Again, additional cooling may be implemented(e.g., via a reactor coolant system) to facilitate precipitation of thePPS polymer. The PPS polymer product 16 may then be separated from theother components in the reactor 14.

An alternative to a water-quench is to instead quench the polymerizationby adding an organic solvent, such as N-methyl pyrrolidone (NMP) 18, tothe reactor 14. This may be beneficial, for example, where too muchwater exists in the reactor 14 prior to quench and a where awater-quench would give excessive particle size of the precipitatingPPS. Such an excessive particle size may cause downstream handlingproblems, for example. Thus, NMP 18 may be added instead of water 12 toquench the reaction and to reduce the particle size of the PPS. Itshould be noted that the present techniques may be employed to determinethe amount of water existing in the reactor 14 prior to quench, and thuswhether an NMP quench is appropriate (or whether to implement a lesstypical combination quench employing both water 12 and NMP 18). Itshould also be noted that other factors may influence the decision ofwhether to water quench or NMP quench.

Another alternative is to cool the reaction, not by quenching, butthrough flashing of the organic solvent (e.g., NMP) that may exist inthe reactor 14. Such flashing may be accomplished, for example, byreducing the pressure of the reactor 14, or by discharging the contentsof the reactor 14 to a lower pressure, and the like. As indicated,relevant equipment in PPS manufacturing systems 10 employing flashtermination may be significantly different than those employing quenchtermination. Nevertheless, it may be beneficial to employ the presenttechniques to determine the amount of water existing in the reactor 14prior to flashing the NMP in the reactor 14 to adjust the conditions ofthe flash, for example.

Finally, regardless of whether the reaction mixture is water-quenched,NMP-quenched, or NMP-flashed to terminate the polymerization, water 12may also be added after termination to wash the PPS before the PPSleaves the reactor 14. Additionally, the PPS 16 discharged from thereactor 14 may also be washed with water. However, these water washestypically do not affect the particle size of the PPS.

B. Polymerization

As mentioned, PPS may be produced by the condensation polymerization ofa sulfur source, such as sodium sulfide (Na₂S) 20 with a dihaloaromaticcompound, such as para-dichlorobenzene (DCB) 22, in a polymerizationreactor 14. Other polymerization modifiers/additives 24, such as sodiumacetate, may be added to the reaction mixture. The polymerization isgenerally exothermic and thus the polymerization reactor 14 may beequipped with a jacket and/or internal cooling coils, which may besupplied with a cooling medium, such as oil, ethylene glycol, propyleneglycol, water, and other heat transfer fluids. Finally, agitation of thereaction mixture, such as through the use of a reactor stirrer oragitator, may advance the polymerization by improving contact of thereactants, improving heat transfer, dispersing the aqueous and organicphases, and so forth.

The sodium sulfide 20 may be supplied in the form of aqueous sodiumhydrosulfide (NaSH) 26 and aqueous sodium hydroxide (NaOH) 28. Theseaqueous feedstocks or pre-reactants may be dehydrated in the presence ofan organic solvent, such as NMP 18, in a feed dehydration vessel orreactor 30 before polymerization takes place. The temperature at whichthe dehydration is conducted generally ranges from about 100° C. toabout 240° C. The pressure will generally range from slightly aboveatmospheric up to about 30 psig.

C. Termination and Recovery

As mentioned, termination may be accomplished by allowing thetemperature of the polymerization mixture to fall below that at whichsubstantial polymerization occurs, typically below 235° C. Aftertermination of the polymerization reaction the PPS polymers may berecovered by conventional techniques, i.e., filtration, washing, flashrecovery, and so forth. Following the typically batch polymerization inthe reactor 14, as discussed, the PPS in the reactor can either beflashed or quenched to obtain the desired polymer type or properties ofthe PPS polymer product 16. Flash-type polymer, in this example, may beformed through flashing the post-reaction mixture to an atmosphericpressure blender where the majority of the NMP is removed. Quench-typepolymer may be formed through cooling the reaction mixture by addingadditional NMP 18 and allowing the polymer to crystallize as smallgranules, or by adding water 12 and allowing the polymer to crystallizeas relatively larger granules. Subsequent to particle formation, themajority of the NMP and/or water may be removed from the quench-typepolymer through the use of a shaker screen, for example. The quenchedpolymer may be additionally washed with NMP 18 and/or water 12. The NMPused in the various processes may be recycled after being purified viadistillation.

D. PPS Polymer and Downstream Processing

After bulk solvent removal, the PPS polymer is generally washed toremove residual impurities including the reaction modifier (if present),by-product sodium chloride (salt), and residual NMP. The polymer may bewater-washed with organic acid or inorganic (e.g., calcium source)additives, depending on the specific requirements. Further, the purifiedpolymer is typically dried. The washing and drying of the PPS polymermay take place in the polymerization reactor 14, in associated equipmentin the immediate area of the reactor 14, in downstream resinhandling/curing systems 31, and so forth.

As used herein, PPS comprises at least 70 mole %, and generally 90 mole% or more of recurring units represented by the structural formula:

and may comprise up to 30 mole % of recurring units represented by oneor more of the following structural formulas:

The dried PPS polymer, whether produced on a pilot scale or commercialscale, may be further processed with special washes, blending, curing,and so forth, as referenced in block 31. For example, the polymer may becured through cross linking and/or chain extension by heating attemperatures above about 480° C. in the presence of freeoxygen-containing gas. Moreover, agents that affect crosslinking, suchas peroxides, crosslinking accelerants, and/or crosslinking inhibitors,may be incorporated into the PPS. Such cured PPS polymer generally hashigh thermal stability and good chemical resistance, and are useful, forexample, in the production of coatings, films, molded objects andfibers. Further, as referenced in either block 31 or 32, and eitheron-site or at separate facilities, the PPS polymer may be blended withvarious additives, such as polymers, fiber reinforcements, glass andcarbon fibers, minerals, fillers, pigments, nucleating agents,antioxidants, UV stabilizers, heat stabilizers, carbon black, metaldeactivators, lubricants, plasticizers, corrosion inhibitors, moldrelease agents, titanium dioxide, clay, mica, processing aids,adhesives, tackifiers, and the like.

The PPS may be may be heated and molded into desired shapes andcomposites in a variety of processes, equipment, and operations, asreferenced in block 32. For example, as will be appreciated by those ofordinary skill in the art, the PPS polymer may be subjected to heat,compounding, injection molding, blow molding, precision molding,film-blowing, extrusion, and so forth. Further, additives, such as thosementioned above, may be blended or compounded with the PPS polymer. Theoutput of such techniques may include, for example, polymerintermediates or composites including the PPS polymer, and manufacturedproduct components or pieces formed from the PPS polymer, and so on.These manufactured components may be sold or delivered directly to auser. On the other hand, the components may be further processed orassembled in end products, for example, in the industrial, consumer,automotive, and electrical/electronic industries, as referenced in block33. Many diversified applications and uses may benefit from theadvantageous properties of PPS, and thus an assortment of components orproducts having PPS polymer may be manufactured or assembled in thedifferent processes and operations represented by blocks 32 and 33.

E. Applications and End-Uses of PPS Polymer

A wide range of appliance products or components incorporating PPSpolymer include, for example, electric blanket thermostats, fry panhandles, hair dryer grills, coffee warmer rings, curling ironinsulators, steam iron valves, toaster switches, clothes dryer switches,clothes washer pumps, dishwasher pumps, non-stick cookware coatings, andmicrowave oven turntables, to name a few. Exemplary business applianceproducts of PPS include printer paper guards, copier gears, fax machineheads, and medical/scientific instrument components. Household andautomotive lighting products constructed of PPS include, for example,reflectors, reflector housings, bulb housings, socket bases, and ballastcomponents.

PPS applications in automotive brake systems include anti-lock brake(ABS) motor components, electric brakes, ABS brake pistons, boosterpistons, and valve bodies. Automotive coolant system applications of PPSpolymer include heater core tanks, thermostat housings, water pumpimpellers, extension tubes, valve components, water inlet/outletconnections. Further, automotive electrical system componentsincorporating PPS include, for example, alternator components, switches,connectors, ignition components, motor brush cards, and sensors. Fuelsystem applications include fuel flow sensors, fuel pump components,throttle bodies/deactivator, fuel line connectors, fuel rails, and fuelinjector bobbins, to name a few. Also, powertrain/transmissioncomponents formed from PPS may include lock-up collars, servo pistonsand covers, engine gasket carriers, seal housings, shift cams/forks,stators, and transmission pistons.

Electrical and electronic applications of PPS cut across a wide range ofresidential, commercial, and industrial uses, and include, for example,applications in computer systems, instrumentation and control systems,power supply systems, and so on. More specific examples of componentsincorporating PPS include electrical connectors, terminal blocks,electrical relays/switches (e.g., relay contact bases), circuit breakerhousings, and high temperature housings for electrical components,electronics packaging (e.g., capacitor encapsulation housings), computermemory module sockets, chip carrier sockets, hard disk drive components,to name a few.

PPS may be incorporated in a variety of components and products incommercial and industrial applications. For example, Heating,Ventilation, and Air Conditioning (HVAC) applications of PPS includecompressor mufflers, flue collectors, secondary heat exchanger headers,fuel oil pumps, hot water circulation components, power vent components,thermostat components, and so on. Other exampled of industrialapplications of PPS include centrifugal pump impellers, chemical pumpvanes, corrosion resistant coating, and filter bags for flue gas in coalburning plants.

F. PPS Polymerization Reactor

FIG. 2 illustrates a diagrammatical representation of an exemplarypolymerization reactor area 34 including the polymerization reactor 14of FIG. 1 and a shaker screen 36 for removing undesirable solids 38 fromthe reactor mixture 40 to give the PPS polymer product 16. The liquidlevel of the mixture 40 in the reactor 14 is designated by referencenumeral 42. In the mixture 40, the depicted larger particles representthe PPS polymer product 16. In contrast, the depicted small particlesrepresent undesirable solids 38, such as salt and slime. During thepolymerization, however, the PPS polymer 16 is typically dissolved inthe reactor mixture 40 (primarily in the organic phase) and is generallynot precipitated until the mixture 40 is cooled.

Normally, the polymerization is exotheromic, and thus means for removingheat may be required. In the illustrated embodiment, a reactor jacket 44removes heat from the reactor contents (e.g., reactor mixture 40).Cooling coils within the reactor may also be employed to remove heatfrom the reactor mixture 40. A variety of cooling mediums, such as oiland other heat transfer fluids, may be supplied to the reactor jacket 44and to the internal cooling coils. In this example, the cooling mediumis oil, with the oil supply (OS) designated by reference numeral 46, andthe oil return (OR) designated by reference numeral 48. An agitator 50may also be employed to facilitate heat transfer, as well as, to promotecontact of the reactants and to help keep the reactor mixture 40(including the PPS) in solution. The agitator 50 may comprise a motor52, a drive 54, a shaft 56, an impeller 58, and the like. The agitator50 may also employ a seal, such as a single or a double mechanical seal.A variety of agitator 50 (or stirrer) configurations may be implemented.

The water 12 that may be used for quenching and other functions, such aswashing, is shown introduced at the top of the reactor 14. The variousfeeds, such as the NMP 18, DCB 22, and Na₂S 20, are illustrated asintroduced on the top head of the reactor 14. However, the feed entrypoints may be configured on any suitable part of the reactor 14.Moreover, flow equipment, such as control valves and internal devices(e.g., nozzles, sprayers, spargers, dip tubes), and so forth, may beemployed. For example, it may be beneficial to employ an internal diptube to introduce organic compounds to the reactor 14.

To measure process variables, a variety of instrumentation known tothose of ordinary skill in the art may be provided. For example, atemperature element 60, such as a thermocouple or resistance temperaturedetector (RTD), may be inserted directly into the reactor 14 or into athermowell disposed in the reactor 14. Temperature indication may beaccomplished, for example, with a local gauge coupled to the temperatureelement 60. In addition or in lieu of a gauge, a temperature transmittercoupled to the temperature element 60 may transmit a temperature signalto a processor or control system 62, such as a distributed controlsystem (DCS) or a programmable logic controller (PLC), where thetemperature value may be read by an operator and/or used as an input ina variety of control functions. For example, as discussed below, thetemperature indication may be used in the control of the flow rateand/or temperature of the cooling medium (e.g., heat transfer fluid)through the reactor jacket 44 and/or cooling coils to control thereactor temperature. The temperature indication may also be used in thedetermination of the amount of water in the reactor 14 and in the amountof quench water to add to the reactor 14, and so on.

Further, a pressure element 64, such as a diaphragm or Bourdon tube, maybe installed on the reactor 34 to measure pressure. A local gauge maycouple to the element 64 to indicate the measured pressure. In additionor in lieu of a gauge, a pressure transmitter coupled to the pressureelement 64 may transmit a pressure signal to the control system 62.Thus, as with temperature indication, the indication of reactor 14pressure may be read locally or remotely by an operator, used todetermine the amount of water in the reactor 14, the desired amount ofwater 12 for quenching, and used in a variety of control functions viathe control system 62.

Additionally, the reactor level 42 may be measure by a level element 66,such as the differential pressure meter represented in the illustratedembodiment. Other exemplary level elements 60 may include a variety ofsensors, such as capacitance or inductance probes inserted into thereactor. As with reactor 14 pressure and temperature, local or remotelevel indication may be employed. The indicated level may be used in thedetermination of the amount of water in the reactor 14, the amount ofquench water to add to the reactor 14, and as input for various controlpurposes via the control system 62, for example.

A variety of other instrumentation and controls may be employed aroundand on the reactor 14. For example, the flow rate of cooling mediumthrough the reactor jacket 42 and/or coils may be measured with a floworifice or mass flow meter disposed on the inlet and/or outlet conduits.The flow rate of cooling medium may be full-open or controlled(automatically or manually) via the control system 62 and/or appropriatevalve configurations. The desired flow rate may be set to asubstantially constant mass or volumetric flow rate, or may be varied tocontrol temperature of the cooling medium return 48 and/or thetemperature of the reactor 14, for example.

Further, the metering of the reactor 14 feeds (e.g. water 12, NMP 18,Na₂S 20, and DCB 22 feeds) are also typically measured and controlled.Such flow measurement may be accomplished, for example, with a flowtotalizer (including mechanical control), or with a mass flow meter orflow orifice (e.g., using differential pressure). Moreover, the flowindication may be based on change in the reactor level 44, and so on.The reactor 14 feeds may be controlled locally or remotely, automatic ormanually, and with manual valves or automatic control valves, forexample.

In general, a control system 62 and other processor-based systems maycontrol a range of operations in the PPS manufacturing system 10, suchas those operations represented in both FIGS. 1 and 2. As will beappreciated by those of ordinary skill in the art, the control system 62may be configured with the appropriate hardware and software (e.g.,code). Further, and in particular, the control system 62 may beconfigured with hardware/software to automatically read measurements ofreactor 14 pressure, temperature, and level, to automatically calculatethe amount of water in the reactor 14, and to automatically calculatethe desired amount of quench water 12. The control system 62 may alsoautomatically facilitate control the addition of quench water 12 to thereactor 14 via suitable control schemes, for example. Such schemes mayrely on software logic and code, as well as on equipment, such ascontrol valves, conduits, instrumentation, etc.

G. PPS Production Method

Referring to FIG. 3, a block diagram of an exemplary PPS productionmethod 68 is depicted. Initially, feedstocks with significant water maybe dehydrated in a vessel or a reactor (block 70). Then, the reactantsand other components, such as the organic solvent, may be contacted in apolymerization reactor (block 72). After polymerization of the reactantsto produce the PPS in the reactor 14 (see FIG. 1), it may be desired toterminate the polymerization (block 74). At this point, the amount ofquench water for terminating the polymerization may be determined (block76). As discussed, the PPS properties are impacted by the total amountof water in the reactor (existing water plus quench water), and thus itis desirable to determine the amount of water existing in the reactorprior to quench to determine the amount of quench water to add. Therelationship or correlation between the total amount of water in thereactor during the quench versus the PPS particle size is generallyknown. After the amount of quench water is determined, then the watermay be added and the reaction quenched (block 78). It should be notedthat additional cooling of the reactor contents, such as by lowering thetemperature of the cooling medium in the reactor jacket and/or coils,may be implemented after the quench water is added to facilitatebringing the PPS polymer out of solution.

It should also be noted that the amount of water existing in the reactorprior to quench may be adequate to give relatively large PPS particles.Thus, NMP, instead of water, may be used to quench the reaction. Inother words, the calculated amount water in the reactor prior to quench,using the present techniques, may call for no addition of quench water,but instead indicate that a NMP quench is beneficial in lieu of a waterquench. Finally, it should be emphasized that the order of the differentactions of the production method 68 depicted in FIG. 3 may vary.

IV. Determination of the Amount of Quench Water

In general, the determination of the amount of quench water may utilizethe vapor liquid equilibrium (VLE) of the polymerization mixture. Aspecific relationship that may be employed is Dalton's Law of PartialPressures, which states that the total pressure of a mixture is equal tothe sum of the individual-component partial pressures:

Dalton's Law of Partial Pressures

P=p* _(A) +p* _(B) +p* _(C)+ . . .where P it the total pressure and p* is the partial pressures of theindividual components. For example, in the present context, the partialpressures of the individual components (e.g., water, NMP, etc.) in thereactor 14 mixture at the reactor temperature sum to equal the reactortotal pressure. As discussed below, this relationship may be used tocalculate the water concentration in the reactor 14 mixture prior toquench.

The calculation may assume the reaction mixture to be ideal, orconversely, may take into account non-ideal behavior of the mixture,depending on the desired accuracy and/or the conditions of the mixture.As will be appreciated by those of ordinary skill in the art, exemplarycorrections for non-ideal behavior include the use of Van der Waalsconstants, activity coefficients in the liquid phase, pure componentfugacities in the vapor and liquid phases, virial equations of state,the Benedict-Webb-Rubin equation, the compressibility factor (equationof state), and so forth.

A. Calculation of the Water Content in the Polymerization Reactor

1. The Use of Raoult's Law to Solve for the Mole Fraction of Water

In one embodiment, the calculation assumes that reaction mixture is anideal binary mixture of water and the polar organic compound (e.g.,NMP). Further, in this example, the calculation assumes that vapor andliquid phases are in equilibrium, and thus the individual-componentpartial pressures equal the individual-component (or pure-component)vapor pressures. Accordingly, the Dalton's Law of Partial Pressures maybe reduced to Raoult's Law:

Raoult's Law

P=P° _(A) x _(A) +P° _(B) x _(B)where P is the total pressure (e.g., reactor pressure), P°_(A) andP°_(B) are the pure component vapor pressures (e.g., of water and NMPrespectively), and x_(A) and x_(B) are the mole fractions of the twocomponents (e.g., water and NMP) in the liquid phase. And because x_(B)may be expressed as 1−x_(A) in a binary system, the mole fraction ofwater, x_(A), may be solved:

Mole Fraction of Water Solved

x _(A)=(P−P° _(B))/(P° _(A) −P° _(B))

Thus, the mole fraction of water may be calculated based on the total(reactor) pressure P, and the pure-component vapor pressures of P°_(A)(water) and P°_(B) (NMP) at the system (reactor) temperature. Therefore,the two basic inputs are reactor pressure and reactor temperature, whichare both measured values. The pure-component vapor pressures may bedetermined using the reactor temperature and a suitable vapor pressureequation, such as Antoine's equation:

Antoine's Equation

Log₁₀ P°=A−B/(T+C)where P° is the vapor pressure, and A, B and C are Antoine coefficientsand vary from substance to substance. The Antoine coefficients(constants) tabulated for water, for example, are A=7.96681, B=1668.21,and C=228.0 for system temperatures, T, in the range of 60 to 150° C.and for vapor pressures, P°, in mm Hg or torr. The Antoine equation isaccurate to a few percent for most volatile substances (with vaporpressures over 10 torr).

Further, the pure component vapor pressures (i.e., for both water andNMP) calculated with the Antoine's equation are only a function of thereactor temperature T. For the calculation of quench water, the vaporpressures may typically be calculated based on the reactor temperatureimmediately prior to quench. However, the calculation methodologiesencompassed by the present techniques for vapor pressures and for theamount or concentration of water in the PPS reactor may be employed atany point in process time, i.e., before polymerization, duringpolymerization, immediately prior to quench, during quench, immediatelyafter quench, long after quench, during washing of the PPS polymer, andso forth. Such calculations may take into account additional variables,such as the presence of precipitated solids, the presence of otherliquid components, the existence of non-ideal conditions, and so forth.

Furthermore, other suitable equations may be utilized for determiningthe pure component vapor pressures. For example, as will appreciated bythose of ordinary skill in the art, the Clausius-Clapeyron equation, InP=−ΔH_(vap)/RT+C, where R is the gas constant and C is a materialconstant, may be used to calculate the pure component vapor pressures ofboth NMP and water, and is a function of the reactor temperature T, andthe heat of vaporization ΔH_(vap). Thus, if this equation is employed,the heat of vaporization may be determined at the temperature ofinterest, or if empirical data is available, the Clausius-Clapeyronequation may provide for a graphical solution (as is apparent by thelinear form of the equation plotted on a logarithmic axis). Othersources of pure-component vapor pressure data include databases, such asdatabases generated by the AICHE Design Institute for PhysicalProperties (DIPPR). These types of databases may provide values of thepure-component vapor pressures for NMP and water at the reactortemperature of interest (i.e., immediately prior to quench). Inconclusion, it should be emphasized that many methods may be utilized todetermine the pure-component vapor pressures.

2. Subtraction to Give the Amount of Quench Water

With the fraction of water calculated, the quench water amount may thenbe determined by subtracting the amount of existing water from thedesired total amount of water during the quench. The data may beconverted to accommodate the desired form or units of the calculation,which may employ (1) concentrations, e.g., mole fraction, mass fraction,etc., or (2) mass, e.g., kilograms, pounds, etc., or (3) volume, e.g.,gallons, liters, etc., and so forth. In sum, the present techniquedetermines the amount of quench water to add to a polyphenylene sulfide(PPS) polymerization reactor to control particle size and otherproperties of PPS in the reactor more consistently.

B. A Method for Calculating the Amount of Quench Water

FIG. 4 depicts a method 76 that corresponds to block 76 of FIG. 3 andwhich determines the amount of quench water (or other similar quenchfluid) to add a polymerization reactor, such as the polymerizationreactor 14 depicted in FIG. 1. In this example, the reactor 14 mixtureis assumed to be an ideal binary mixture of water and NMP with saturatedvapor. Initially, the temperature of the reactor 14 is measured (block76A) and used to calculate (block 76B) the pure-components vaporpressures of water (P°_(A)) and NMP (P°_(B)) in the reactor. Thepure-component vapor pressure calculation may be performed withAntoine's Equation, for example. Additionally, the pressure of thereactor 14 may be measured (block 76C). Based on this measured pressureof the reactor 14, and on the calculated pure-component vapor pressures,the water fraction in the reactor fluid may be calculated (block 76D)using Raoult's Law, for example, as discussed above.

In certain applications, it may be beneficial to evaluate the water inthe reactor as a concentration in terms of fractions or percents (seeFIGS. 5 and 6). For example, where the fluid level in the reactor 14(see FIGS. 1 and 2) is substantially the same from polymerization topolymerization, or where water concentration is a more meaningfulmeasure than the absolute amount of water (e.g., where historical datais based on concentration), the quench water determination may be baseddirectly on the concentration (e.g., mole fraction) of water existing inthe reactor, as referenced by block 76E. It should be noted that theconcentration of water in the reactor 14 may be converted to variousrepresentations, such as weight percent or mass fraction of water (basedon the densities of water and NMP), volume of water (based on the totalliquid volume in the reactor 14), mass of water (based on the totalliquid volume, and the densities of water and NMP), and so forth.

In addition, the total liquid in the reactor may be measured (block 76F)and the absolute amount of water (i.e., gallons or pounds) in thereactor calculated by multiplying the water fraction by the total liquid(block 76G). The total amount of fluid in the reactor may be directlymeasured, for example, by a level element or indicator, such as a sightglass or differential pressure meter, with the level indication readilyconverted to a volume indication based on the geometry of the reactor14. The amount of quench water to add the reactor 14 may then becalculated by subtracting the amount of water existing in the reactorfrom the total amount of water desired for terminating the reaction (togive desired PPS particle size), as referenced by block 76I. Asdiscussed, the total amount of water desired may be based on knowncorrelations between water and PPS particle size (e.g., average diameterin microns).

Finally, as discussed, it should also be clarified that all actions,ranging from the measuring of process variables to performing thevarious calculations to physically adding the quench water to thereactor 14, may be performed manually or automatically, or a combinationthereof. Automatic reading of measurements, performance of calculations,and control of the process may be accomplished, for example, via thecontrol system 62 (e.g., DCS or PLC) having the appropriate softwarecode, hardware, and equipment. As will be appreciated by those ofordinary skill in the art, a variety of processors, sensors,instrumentation, valve arrangements, control schemes, etc., such asthose previously discussed, may be employed to control the variousfunctions of the PPS production and the present techniques. Moreover, itshould be emphasized that the order of the different actions of themethod 76 depicted in FIG. 4 may vary.

C. Calculated Mole Fraction Increase Versus the Amount of Water Added

FIG. 5 is a representative plot 80 of the calculated increase 82 of molefraction of water in the reaction mixture versus the actual amount 84 ofquench water added to the reaction mixture. Using the reactortemperature and pressure, and Raoult's Law, as discussed above, the molefraction of water in the reactor prior to quench and after quench iscalculated. The difference between these two mole fraction values givesthe increase 82 in the mole fraction of water in the reactor 14. Theclustering of the data, as well as the realized linear relationshipbetween this increase 82 versus the actual amount 84 of water addedsupports the use of the present techniques. A linear relationship isexpected theoretically with the form of the Raoult's Law equation andwith an ideal binary mixture (see part A of Section IV).

As for the representations of the plotted data, six points 86 correspondto no quench water added, leaving an expected calculated value ofapproximately no increase (zero increase) in the water in the reactionmixture. For one gallon of quench water added to the reaction mixture,two points 88 show a calculated increase in the mole fraction of waterof approximately 0.07. Further, at two gallons of water added to thereaction mixture, seven points 90 correspond to an increase in thereaction mixture of about 0.12 mole fraction of water. The approximatelinear relationship of the calculated mole fraction increase 82 with theamount 84 of quench water added is depicted by a straight line 92.

D. PPS Particle Size Versus the Mole Fraction of Water During Quench

FIG. 6 illustrates a representation of a plot 94 of the average particlesize diameter 96 in microns versus the mole fraction 97 of water (totalwater) in the reaction mixture after the quench water has been added.The particle size 96 values are measured. The mole fraction 97 (totalwater) values are calculated based on the approach above of usingRaoult's law and the reactor temperature and pressure. Three sets ofdata, represented by circles 98, triangles 100, and squares 102, areplotted based on three different rotation speeds of the reactor agitatorof 350 revolutions per minute (rpm), 400 rpm, and 450 rpm, respectively.

The first set, depicted as circles 98 and based on a 350 rpm agitationspeed. At calculated mole fractions of water of about 0.18 and 0.34, themeasured PPS particle sizes (average diameters) are about 550 micronsand about 1600 microns, respectively. The second set of data aredepicted as triangles 100 and based on a 400 rpm agitation speed. Thethird set of data (two points), depicted as squares 102 and based on anagitation speed of 450 rpm, show a PPS particle size 96 of about 1500microns at a mole fraction 97 of water of about 0.21. In oneinterpretation, the relationship between particle size 96 versus themole fraction 97 increases with a steeper slope at lower mole fractions97, and becoming asymptotic at higher mole fractions 97. In other words,if the data are fit to a single curve, the single curve representingparticle size 96 as a function of mole fraction 97 of water wouldincrease somewhat linearly at a relatively steep slope at lower molefractions 97 of water, and then flatten at higher mole fractions 97 ofwater.

It has been observed that the relationship between particle size and thecalculated water mole fraction values improves at lower agitationspeeds. In other words, less scatter of data is generally realized atagitation speeds below about 500 rpm. Finally, it should be noted thatthese data sets and other similar types of data may be utilized manuallyby a human operator or engineer, or automatically in a control scheme,for example, to decide how and what aspects of the present techniques toemploy.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and will be described in detail herein. However,it should be understood that the invention is not intended to be limitedto the particular forms disclosed. Rather, the invention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the invention as defined by the following appended claims.

1. A method for producing polyphenylene sulfide (PPS) polymer,comprising the acts of: conducting a PPS process to polymerize reactantsin a reaction mixture in a vessel to form PPS polymer in the vessel;measuring a pressure and a temperature in the vessel; and determining anamount of a quench fluid to add to the reaction mixture, wherein theamount of quench fluid is correlative to at least one of the pressureand the temperature.
 2. The method as recited in claim 1, wherein theact of conducting a PPS process comprises the acts of: adding reactantscomprising a sulfur source and a dihaloaromatic compound to the vessel;and adding a polar organic compound to the vessel.
 3. The method asrecited in claim 2, wherein the sulfur source comprises sodium sulfide(Na₂S), the dihaloaromatic compound comprises p-dichlorobenzene (DCB),and the polar organic compound comprises N-methyl-2-pyrrolidone (NMP).4. The method as recited in claim 1, wherein the act of determining theamount of quench fluid comprises the act of calculating a fraction ofwater in the reaction mixture based on a vapor liquid equilibrium (VLE)of the reaction mixture.
 5. The method as recited in claim 4, whereinthe quench fluid comprises water.
 6. The method as recited in claim 1,comprising the act of measuring a liquid level in the vessel, whereinthe amount of quench fluid is correlative to the liquid level.
 7. Amethod of manufacturing a PPS polymer, comprising the acts of:contacting reactants in a reactor to form the PPS polymer in thereactor; measuring pressure and temperature of the reactor; determiningan amount of quench water to add to the reactor correlative to thepressure or the temperature, or a combination thereof; and quenching apolymerization of the PPS polymer in the reactor by adding the quenchwater to the reactor.
 8. The method as recited in claim 7, whereindetermining an amount of quench water to add to the reactor is based ona vapor liquid equilibrium (VLE) in the reactor.
 9. The method asrecited in claim 7, wherein determining an amount of quench watercomprises the act of calculating an amount of water in the reactor priorto quench based on variables comprising the pressure in the reactor andthe temperature in the reactor.
 10. The method as recited in claim 7,wherein a total amount of water in the reactor during quench is relatedto a particle size of the PPS polymer.